docs: def ssh(ctx, cluster_id, key_file):
      """SSH login to EMR master node"""
      session = create_session(ctx.obj['AWS_PROFILE_NAME'])
  
      client = session.client('emr')
      result = client.describe_cluster(ClusterId=cluster_id)
      target_dns = result['Cluster']['MasterPublicDnsName']
      ssh_options = '-o StrictHostKeyChecking=no -o ServerAliveInterval=10'
      cmd = 'ssh {ssh_options}  -i {key_file} hadoop@{target_dns}'.format(
          ssh_options=ssh_options, key_file=key_file, target_dns=target_dns)
      subprocess.call(cmd, shell=True)